Light-emitting diodes (LEDs) are used as a kind of solid-state light source. Compared with conventional lighting, such as incandescent or fluorescent lamps, its advantages are compactness, high efficacy, good color, various and variable color, etc. LEDs are widely used in indoor lighting, decoration lighting and outdoor lighting. Some of these applications require the output light of the LEDs to be adjusted from 1% to 100% of the maximum light output.
In the field of drivers, drivers are known in many different topologies. Some of these topologies e.g. buck converter, boost converter, buck-boost converter can be configured in a synchronous topology. This particularly results in a high efficient driver.
In the field of LED drivers, synchronous converters are well known for driving LED loads. US 2016/0036312 discloses a synchronous buck converter comprising a first switch, a second switch and an inductor. At the beginning of a cycle, the first switch is turned on, and current rises in the inductor. At the end of the rise, the first switch is turned off and the second switch is turned on consecutively and the current decays in the inductor. The second switch can be turned off at the time the current returns to zero. The first switch is then turned on again when a preset value associated with the resonant interval across the switching node exceeds a predefined value.
US 2014/0070780 discloses a control circuit for controlling a switching transistor and a synchronous rectifying transistor of a switching regulator and includes: a bottom detection comparator configured to assert an on signal; a timer circuit configured to generate an off signal; a zero current detector configured to assert a zero current detection signal; and a driving circuit configured to receive the on signal, the off signal and the zero current detection signal, and (i) turn on the switching transistor and turn off the synchronous rectifying transistor when the on signal is asserted, (ii) turn off the switching transistor and turn on the synchronous rectifying transistor when the off signal is asserted, and (iii) turn off the switching transistor and the synchronous rectifying transistor when the zero current detection signal is asserted.
U.S. Pat. No. 6,151,233 discloses a switching power circuit wherein adopting the synchronous rectifying system, when a first switch is cut-off, current IL of an inducing element is maintained by a commutating diode, and the inducing element releases an energy which was stored in a conduction period of the first switch. A second switch connected in parallel to the commutating diode is conducted so as not to be overlapped with the conduction period of the first switch. In the conduction period of the second switch, the current IL does not flow through the commutating diode, and it is possible to prevent lowering of efficiency caused by forward voltage drop. An inducing element current detecting circuit monitors the current IL and, when the current IL is reversing its direction, instructs a control circuit to cut-off the second switch. As a result, no reverse current flows through the inducing element even when the load is small, thus realizing a switching power circuit always having high efficiency.